Most likely inaccurate giant nodosaur.

Here´s the giant Mussentuchit nodosaur that supposedly reached 10 meters in length (Scaling with that gives 13.94 tonnes of weight).

There are a few problems with this drawing: 1. The specimen was actually a Peloroplites , meaning that it would look less like Gastonia than depicted here, and more like a Polacanthus. 

Secondly, the 10 meter specimen was one out of supposedly many 7 meter specimens. Except that the 7 meter specimens might actually be 5.5 meters, and the ´10 meter´ specimen could be 7 meters. This would make more sense in my opinion, and gives a weight of ~4.8 tonnes. Still a huge beast, but not quite this big. Maybe.
Alternatively, the rumours could be true, and then we do have a 10 meter Peloroplites overlord.

In either case, it would be a very well armored tank that no well-thinking Siats would try to take on, when adult.

Reference by and thanks for :icon105692: for telling me about it.